1. Field of the Invention
The present invention relates to a process for fabricating a thin film semiconductor device. In addition, the present invention is concerned with a thin film semiconductor device produced using the process and an apparatus having mounted the thin film semiconductor device.
2. Description of Related Art
Currently, in a TFT (thin film transistor) for use in transmissive LCD (liquid crystal display), polysilicon or amorphous silicon is mainly used. A TFT using thin film single-crystalline silicon as a material has excellent properties such that the current driving ability is high, a variation of the threshold voltage Vth is small, and the like. As a method for producing the TFT, for example, a method in which a transistor and an isolation region are formed on an SOI (silicon on insulator) substrate and an insulating film is etched using hydrofluoric acid for lift-off has been proposed. For, example, please refer to the following document.
Japanese Patent Application Publication No. Hei 9-312349
In addition, currently, as a transistor having a structure for improving the current driving ability, a double gate thin film single-crystalline silicon transistor is being developed. The transistor having this structure can be produced by, for example, a bonding method. This production method has a feature such that a back gate is preliminarily incorporated into a laminate substrate to form an SOI substrate. However, this transistor has technical problems in that self-alignment cannot be achieved and the production cost is increased.
In the above problems, with respect to the self-alignment structure, for example, IBM has proposed a method called a Fin FET Structure method. This production method has a feature such that a gate is etched from the side of an SOI layer which is vertical. This method enables the gate lengths on both sides to be completely equal to each other, so that a double gate transistor having ideal electrical properties can be produced.
However, any methods have a problem in that the production cost is high. Further, the production methods mentioned above also have a problem concerning mass production.